1. Field of the Invention
The present invention relates to a data writing method for Mask Read Only Memory, and more particularly to a Mask Read Only Memory using doses of four different ion implantations as the bit data writing method.
2. Description of the Prior Art
Mask Read Only Memory (MROM) is one type of memory IC. MROM is a memory device that uses the mask to program in LSI (large-scale integrated circuit) chip processing.
Since writing is not necessary, the entire circuit becomes simpler. The basic memory cell also becomes simpler and comprises one MOS transistor. Compared with Random Access Memory (RAM) which allows memory data to be continuously changed, the size of MOS is only a fourth of RAM. For chips with the same size, the memory capacity of MROM is about four times that of RAM. It is an economical method applied in various electronic productions.
The data writing is completed depending on the mask from the user. In order to shorten the TAT (Turn Around Time), the program is usually performed during chip processing. However, the memory cell has a larger area, so that the costs disadvantageously increase.
Therefore, a data writing method for Mask Read Only Memory is provided to overcome the above-mentioned disadvantages, which reduces the required cell area and lowers the bit cost and the size of die under the condition of required density.